Gas turbines engines typically comprise a compressor for an oxidizer such as air, a combustion chamber for combusting the compressed air with a fuel generating hot gas and a turbine for expanding the hot gas and collecting mechanical work.
The turbine in particular has a duct and vanes extending from the casing into the duct and blades extending from a rotor into the duct.
In order to connect the blades to the rotor, the rotor has seats and the blades have roots (usually shaped like fir trees) that are connected into the seats to radially fix the blade position. In addition, in order to fix the axial position of the blades, lock plates are provided connected to both the rotor and the blade.
Since the roots undergo high stress and can be subject to high temperature, for example due to leakages of hot gas from the duct, the roots (but also other rotor and blade parts close to the roots) need to be cooled. For this reason, a chamber is usually provided between the roots and the rotor (i.e. below the roots) and, in addition, a shank cavity is provided between the roots and blade platforms (i.e. above the blade roots).
Cooling air is then typically supplied into each chamber via a cooling channel of the rotor, and from the chamber cooling air is supplied into each shank cavity via passages indented in the sides of the roots, i.e. in the parts of the blades that connect the blades to the rotor.
For this reason the connection surface between the roots and the rotor is reduced; this can cause increased stress in the roots. In addition, since often the cooling channel is indented in terminal parts of the connection surface, stress of the root can be non-uniform over the connection surface axial length. Moreover, since the passages for supplying cooling air from the chamber into the shank cavity have strict constrains deriving from the fact that they are indented in the roots, their configuration could not be optimized for cooling, such that heat removal could, be non-optimal.